Flow structure of the active medium of a HF laser with a radially expanding nozzle unit

Measurements have been made of gasdynamic characteristics of the flow of the active medium as well as energy and spectral characteristics of radiation generated by a continuous chemical HF laser with a radially expanding nozzle unit. Based on the analysis of measurement results, the flow structure of the active medium has been determined, which is formed by the “nozzle–injector” reactant mixing scheme. It has been shown that only a part of the active medium is involved in the radiation generation. Measures for improving the efficiency of its use have been proposed.     

Calculation of the characteristics of a mixing CO2 gasdynamic laser with a nozzle unit of honeycomb construction

A mathematical model of a gasdynamic laser with parallel supersonic mixing of the components and its applications to the choice of the geometrical characteristics of the nozzle unit of honeycomb construction are presented.Notation T static temperature - u velocity - P pressure - molecular weight - e_i average number of vibrational quanta - k amplification ratio for a weak signal - I radiation intensity - _i molar fraction of the component in the mixture - ^* displacement thickness - r, d current radius and diameter of the nozzle - angle of inclination of the generating profile of the nozzle and characteristic temperature - h enthalpy - G flow rate - L characteristic length - A/A* expansion ratio of the nozzle - T_w wall temperature - ¯T_w=¯T_w/T_o temperature factor - =E _a /E_* nozzle efficiency - E stored vibrational energy - X=X/(r_a1 + r_a2) dimensionless coordinate Indices 1 radiating gas stream - 2 exciting gas stream - 0 stagnation value - a, *, values at the cut of the nozzle, in its critical cross section, and beyond the compression shock in the cross section of the nozzle cut Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 53–59, July, 1984.     

High-power HF laser pumped by an electron-beam-initiated chemical nonchain reaction

The development of a high-power HF laser pumped by a chemical nonchain reaction initiated by a radially converging electron beam is reported. A radiation energy of ∼ 115 J with an efficiency of ∼ 8% in terms of deposited energy has been achieved in a mixture with an active volume of ∼ 30 liters. It is shown that because of the high SF₆ density, the total pressure jump in SF₆–H₂(D₂) mixtures caused by the electron beam injection and the chemical reactions is several times smaller than that in the active mixtures of exciplex lasers for the same input energies. This factor considerably facilitates the development of wide-aperture HF and DF lasers with an SF₆ fluorine donor pumped by an electron-beam-initiated chemical nonchain reaction. Pis’ma Zh. Tekh. Fiz. 23, 58–64 (March 12, 997)     

Modeling of the refraction of a laser sheet in transparent radially nonuniform media

The problem of the refraction of a laser sheet in a transparent spherical nonuniformity, for example, in the liquid of a thermal lens, is solved. Equations of the projection of the laser sheet, passing through the nonuniformity, are obtained. It is shown that by using projections of the laser sheet one can determine the sign of the nonuniformity gradient and its order of magnitude, and also establish the parameters of the specified model of the nonuniformity. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 49–52, October, 2006.     

Errors in reproducing the planar-angle unit with a ring laser

Translated from Izmeritel'naya Tekhnika, No. 12, pp. 11–12, December, 1989.     

Experiments with active phase matching of parallel-amplified Multiline HF laser beams by a phase-locked Mach-Zehnder interferometer

Active phase matching of multiline HF laser beams by means of a phase-locked Mach-Zehnder interferometer was demonstrated by locking the interferometer to the central interference fringe at zero optical path length difference. The central fringe could be found by varying the spectral content of the input beam. Laser amplification in one leg of the interferometer decreased fringe visibility without adversely affecting locking. Single-line fringe patterns produced by an array spectrometer (while the interferometer was operated in its scanning mode) were analyzed to show that no significant dispersion occurred in the amplifier. The techniques developed have potential for measuring dispersion mismatch between larger parallel amplifiers. These experiments demonstrated in principle that a number of multiline HF amplified beams can be recombined and phase-matched to produce a high beam quality output beam.     

Shrinkage properties of a modified dental resin composites containing a novel spiro-orthocarbonate expanding monomer

ObjectivesThis study investigated the photopolymerization-induced shrinkage properties of conventional methacrylate-based composites modified by a novel spiro-orthocarbonate (SOC) expanding monomer.MethodsThe epoxy monomer and SOC expanding monomer were added to a methacrylate-based resin matrix at five different ratios ranging from 20 wt.% (SOC + Epoxy) (group 1) to 60 wt.% (SOC + Epoxy) (group 5). Volumetric shrinkage and contraction stress developing after polymerization were measured using X-ray micro-computed tomography and a universal testing machine, respectively.ResultsThe volumetric shrinkage of the resin composite samples ranged from 0.92% (group 5) to 3.85% (control group) 30 min after light curing. Group 5 had the lowest volumetric shrinkage (p < 0.05), followed by groups 4, 3, 2 and 1. The contraction stress of the materials ranged from 1.86 MPa (group 5) to 3.56 MPa (control group). The lowest contraction stress was also observed in group 5, 30 min after curing (p < 0.05).ConclusionIncluding SOC expanding monomer reduced volumetric shrinkage and contraction stress of composites in comparison with conventional methacrylate-based composites.     

Analytical investigation into the powder distribution and laser beam-powder flow interaction in laser direct energy deposition with a continuous coaxial nozzle

The powder distribution and interaction between the laser beam and powder flow affect the deposition quality during the process of laser direct energy deposition with a continuous coaxial nozzle. In this paper, some key analytical formulae related to the laser beam-powder flow interaction are comprehensively deduced and validated. The powder distribution formulae for different regions are first established considering the divergence angles of powder jet. The energy attenuation formulae of laser beam passing through the powder flow are derived considering the change of powder distribution from annular to circular Gaussian modes. The temperature formulae of powder particles passing through the laser beam are derived based on a proposed temperature formula with the solid-liquid phase transition, and the powder temperature is also further analyzed. These formulae are validated by published deposition examples and used to analyze the laser beam-powder flow interaction.     

A modified cohesive zone model for a high‐speed expanding crack

The present work studies a self‐similar high‐speed expanding crack of mode‐I in a ductile material with a modified cohesive zone model. Compared with existing Dugdale models for moving crack, the new features of the present model are that the normal stress parallel to crack faces is included in the yielding condition in the cohesive zone and traction force in the cohesive zone can be non‐uniform. For a ductile material defined by von Mises criterion without hardening, the present model confirms that the normal stress parallel to crack face increases with increasing crack speed and can be even larger than the normal traction in the cohesive zone, which justifies the necessity of including the normal stress parallel to the crack faces in the yielding condition at high crack speed. In addition, strain hardening effect is examined based on a non‐uniform traction distribution in the cohesive zone.     

Study of conjugate heat transfer in the nozzle grid of a gas-dynamic laser

The characteristics of the flow and heat transfer in the nozzle grid of a gas-dynamic laser in the presence and absence of cooling of the blades are studied numerically in a conjugate formulation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 5, pp. 736–743, May, 1987.     

Intracavity generation of radially polarized CO2 laser beams based on a simple binary dielectric diffraction grating

We present experimental results on the intracavity generation of radially polarized light by incorporation of a polarization-selective mirror in a CO(2)-laser resonator. The selectivity is achieved with a simple binary dielectric diffraction grating etched in the backsurface of the mirror substrate. Very high polarization selectivity was achieved, and good agreement of simulation and experimental results is shown. The overall radial polarization purity of the generated laser beam was found to be higher than 90%.     

一种激光探测与波长测定装置的研究

介绍了一种主要用于夜间的激光探测与波长测定装置，它是基于激光在光学劈尖上产生干涉条纹的特点、通过傅里叶变换测定条纹间距来计算激光波长的，测试结果表明该装置在背景光微弱的情况下，性能令人满意，具有一定的实用性。     

Dissolution enhancement of a poorly water-soluble antimalarial drug by means of a modified multi-fluid nozzle pilot spray drier

A spray drier with a modified multi-fluid nozzle was used to prepare microparticles of a poorly water-soluble antimalarial drug, artemisinin (ART), with the aim of improving its dissolution in water. ART was co-spray dried with a hydrophilic polymer, polyethylene glycol (PEG). The differential scanning calorimetry and X-ray diffraction studies showed that the crystallinity of ART decreased after spray drying. Compared to the physical mixture of ART and PEG, the amorphous phase of ART in the spray dried ART–PEG composites increased, which depended on the weight ratio of drug to polymer. The phase-solubility studies revealed that the aqueous solubility of ART was improved by the presence of PEG. The dissolution of ART from the spray dried ART–PEG composites was more rapid than that from their respective physical mixture and the original ART powder. For example, the dissolution of ART from the spray dried ART–PEG composite (1:6) was 6.5 times higher than that from the original ART powder in the first 30 min. In the mathematical modeling, the Weibull and Korsemeyer–Peppas models were found to best fit to the in vitro dissolution data and then the drug release mechanism was considered as the Fickian diffusion.     

Generation of three-dimensional dark spots with a perfect light shell with a radially polarized Laguerre-Gaussian beam

The theoretical analyses in this paper show that a highly focused double-ring radially polarized Laguerre-Gaussian beam with a topological charge of 1 (R-LG(11)) can generate a small three-dimensional (3D) dark spot surrounded by an almost 100% uniform light shell in all directions. The cleanness and size of the 3D dark spot, the uniformity and strength of the light shell surrounding the dark spot, and the light efficiency all depend on the truncation parameter β of the R-LG(11) beam and the numerical aperture (NA) of the system. When β=1.6 and the NA is close to its utmost, an almost 100% uniform light shell surrounding the 3D dark spot can be achieved and the dark spot is very clean. If the NA is lowered but β is increased to 1.95, we can also achieve an almost 100% uniform light shell and light efficiency can reach 90%, but the disadvantage is that the center of the dark spot is not too clean. A not-too-clean 3D dark spot, if the light shell surrounding it is very uniform, is acceptable for many applications. Therefore, 3D dark spots surrounded by a high uniform light shell, generated by simply adjusting the truncation parameter of the R-LG(11) beam and the NA of the system, are useful for superresolution fluorescence microscopy, dark spot microscopy, and the dark spot trap.     

Osteoblast cell adhesion on a laser modified zirconia based bioceramic

Due to their attractive mechanical properties, bioinert zirconia bioceramics are frequently used in the high load-bearing sites such as orthopaedic and dental implants, but they are chemically inert and do not naturally form a direct bond with bone and thus do not provide osseointegration. A CO₂ laser was used to modify the surface properties with the aim to achieve osseointegration between bioinert zirconia and bone. The surface characterisation revealed that the surface roughness decreased and solidified microstructure occurred after laser treatment. Higher wettability characteristics generated by the CO₂ laser treatment was primarily due to the enhancement of the surface energy, particularly the polar component, determined by microstructural changes. An in vitro test using human fetal osteoblast cells (hFOB) revealed that osteoblast cells adhere better on the laser treated sample than the untreated sample. The change in the wettability characteristics could be the main mechanism governing the osteoblast cell adhesion on the YPSZ.